1. Field of the Invention
The present invention generally relates to a small motor vehicle with a power unit that comprises an engine and a belt-driven continuously variable transmission. More particularly, the present invention relates to a structure for mounting the power unit relative to a vehicle frame.
2. Description of the Related Art
Small motor vehicles that are mainly used for commuting or for light-duty business purposes typically have a backbone-type frame. The frame generally comprises a steering head pipe that supports a front fork and a main frame member that extends rearward from the steering head pipe.
The main frame member forms the primary structure of the frame. Brackets are secured to an intermediate portion of the main frame member. The brackets are used to suspend the crankcase of an engine. The brackets protrude downward from the main frame member. The crankcase of the engine has protrusions at its upper front and rear ends. The protrusions extend upward from the topside of the crankcase and are secured to the lower ends of the brackets by bolts. Such a construction is shown in Japanese Published Application No. 2001-0003723, for example.
As shown in the Japanese reference, the joints between the brackets and the protrusions are located between the topside of the crankcase and the main frame member. In such a configuration, because space must be provided between the topside of the crankcase and the main frame member to accommodate the boss parts and the brackets, the distance between the crankcase and the main frame member is unavoidably enlarged.
The vertical position of the engine above the road surface is related to the characteristics of the terrain expected to be encountered. In other words, the engine needs to be sufficiently elevated above the road surface to reduce the likelihood that the engine will contact the road surface during operation. The position of the main frame member is determined by the position of the engine. As such, the main frame member is generally located significantly above the road surface. A seat is supported on the main frame member, which means that the elevation of the seat above the road surface also is relatively high. The relatively high position of the seat can make it difficult for a rider to put both feet on the ground easily while the vehicle is stopped.